1918-19.] Reaction Velocity of Sodium Nitrite on Blood. 151 
calculated in the usual way and the results plotted. Owing to the rapidity 
with which the observations had frequently to be made, great accuracy was 
not possible ; but, as the figures show, the changes were so marked that the 
results are not thereby invalidated. For the same reason it was only 
possible to employ one quadrant of the divided circle ; but as only relative 
results were required, this was no disadvantage. All observations made 
during the change of absorption, with rare exceptions, are shown in the 
graphs. Those made prior to the commencement of any change and 
subsequent to its completion are, for the most part, omitted for the sake 
of simplicity. The sodium nitrite employed was that sold for medicinal 
use, neutralised and standardised against potassium permanganate. 
As previously stated, different samples of blood may react differently 
to small concentrations of sodium nitrite. The differences are not so much 
in the form of the curve when the reaction has commenced, as in a delay 
in the commencement of the action. With four-hundredth normal sodium 
nitrite solution containing 1 per cent, of blood no obvious change occurs 
with average specimens of blood for about one and a half minutes ; then 
a reaction begins, and proceeds very rapidly, almost reaching completion 
within another minute. In some samples of blood, although the reactive 
period has been practically the same, the delay in the commencement of 
the reaction has been shorter ; in others it has been more prolonged. Thus 
in one experiment the reaction did not commence for eleven minutes. The 
cause of this delay in the appearance of the reaction has not been specifically 
investigated, and it is mentioned at this place chiefly to point out that the 
different graphs illustrating the paper, which are for the most part from 
different series of experiments, are not necessarily comparable with one 
another. 
Effect of Concentration of Blood . — The effect of four-hundredth normal 
sodium nitrite on different concentrations of blood is shown in fig. 2. It 
will be observed that the action is delayed by increasing concentration 
of blood. The preliminary dip in the curve with 2 per cent, blood is 
unusual, and a broken line has been inserted to indicate the course more 
commonly followed. This was the only occasion on which a dip of this 
extent was observed. Not infrequently a slight initial fall in the extinction 
coefficient of nitrited 2 per cent, blood is seen, but its significance has not 
been determined. With smaller concentrations of blood it is less common. 
The observations with 0 5 per cent, blood will be noted to be somewhat 
irregular. This is due to the difficulty of matching the hue of the blood 
owing to the relatively slight absorption, and to the fact that from zero up 
to 40° the analysing nicol has to be moved through a considerable arc to 
